U.S. patent number 11,398,553 [Application Number 17/100,543] was granted by the patent office on 2022-07-26 for source/drain features.
This patent grant is currently assigned to TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.. The grantee listed for this patent is Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Chen-Ming Lee, Wei-Yang Lee, Ruei-Ping Lin, Kai-Di Tzeng.
United States Patent |
11,398,553 |
Lin , et al. |
July 26, 2022 |
Source/drain features
Abstract
A semiconductor structure and a method of forming the same are
provided. In an embodiment, a semiconductor structure includes a
first plurality of channel members over a backside dielectric
layer, a second plurality of channel members over the backside
dielectric layer, a first gate structure over and wrapping around
each of the first plurality of channel members, a second gate
structure over and wrapping around each of the second plurality of
channel members, and a through-substrate contact that extends
between the first plurality of channel members and the second
plurality of channel members, between the first gate structure and
the second gate structure, and through the backside dielectric
layer.
Inventors: |
Lin; Ruei-Ping (Hsinchu,
TW), Tzeng; Kai-Di (Hsinchu, TW), Lee;
Chen-Ming (Taoyuan County, TW), Lee; Wei-Yang
(Taipei, TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Company, Ltd. |
Hsinchu |
N/A |
TW |
|
|
Assignee: |
TAIWAN SEMICONDUCTOR MANUFACTURING
COMPANY, LTD. (Hsinchu, TW)
|
Family
ID: |
1000006453741 |
Appl.
No.: |
17/100,543 |
Filed: |
November 20, 2020 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20220165848 A1 |
May 26, 2022 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
29/7855 (20130101); H01L 29/6681 (20130101); H01L
29/1033 (20130101); H01L 29/42392 (20130101); H01L
29/66818 (20130101); H01L 29/66439 (20130101); H01L
29/0673 (20130101); H01L 29/66545 (20130101); H01L
29/78696 (20130101); H01L 29/6656 (20130101); H01L
29/7851 (20130101); H01L 29/775 (20130101); H01L
2029/7858 (20130101) |
Current International
Class: |
H01L
29/66 (20060101); H01L 29/775 (20060101); H01L
29/786 (20060101); H01L 29/423 (20060101); H01L
29/06 (20060101); H01L 29/10 (20060101); H01L
29/78 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO-2020065732 |
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Apr 2020 |
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WO |
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Other References
Liao, Yi-Bo, et al., "Source/Drain Contact Structure", U.S. Appl.
No. 17/093,230, filed Nov. 9, 2020, Assignee: Taiwan Semiconductor
Manufacturing Co., Ltd., 50 pages specification, 57 pages drawings.
cited by applicant .
Lung-Kun Chu, et al., "Self-Aligned Backside Source Contact
Structure", U.S. Appl. No. 17/016,109, filed Sep. 9, 2020,
Assignee: Taiwan Semiconductor Manufacturing Co. Ltd., 31 pages
specification, 17 pages drawings. cited by applicant .
Huan-Chieh Su, et al., "Backside Power Rail and Methods of Forming
the Same", U.S. Appl. No. 16/901,963, Assignee: Taiwan
Semiconductor Manufacturing Co., Ltd., 29 pages specification, 22
pages drawings. cited by applicant .
Pei-Wei Wang, et al., "Method of Forming Backside Power Rails",
U.S. Appl. No. 17/037,274, Assignee: Taiwan Semiconductor
Manufacturing Company, Ltd., 29 pages specification, 16 pages
drawings. cited by applicant.
|
Primary Examiner: Taylor; Earl N
Attorney, Agent or Firm: Haynes and Boone, LLP
Claims
What is claimed is:
1. A semiconductor device, comprising: a first plurality of channel
members over a backside dielectric layer; a second plurality of
channel members over the backside dielectric layer; a first gate
structure over and wrapping around each of the first plurality of
channel members; a second gate structure over and wrapping around
each of the second plurality of channel members; and a
through-substrate contact that extends between the first plurality
of channel members and the second plurality of channel members,
between the first gate structure and the second gate structure, and
through the backside dielectric layer, wherein the
through-substrate contact is spaced apart from the backside
dielectric layer by a bottom epitaxial feature.
2. The semiconductor device of claim 1, further comprising: a first
plurality of epitaxial features in contact with the first plurality
of channel members; and a second plurality of epitaxial features in
contact with the second plurality of channel members, wherein each
of the first plurality of channel members is spaced apart from the
through-substrate contact by one of the first plurality of
epitaxial features, wherein each of the second plurality of channel
members is spaced apart from the through-substrate contact by one
of the second plurality of epitaxial features.
3. The semiconductor device of claim 2, further comprising: a
silicide layer disposed between the first plurality of epitaxial
features and the through-substrate contact; and a bottom silicide
layer disposed between the bottom epitaxial feature and the
through-substrate contact.
4. The semiconductor device of claim 2, wherein a portion of the
through-substrate contact extends between two adjacent epitaxial
features of the first plurality of epitaxial features.
5. The semiconductor device of claim 2, wherein the first plurality
of channel members are interleaved by a plurality of inner spacer
features, wherein the through-substrate contact is in direct
contact with each of the plurality of inner spacer features.
6. The semiconductor device of claim 2, wherein the first plurality
of channel members and the second plurality of channel members
extend lengthwise along a direction, wherein each of the first
plurality of epitaxial feature includes a thickness along the
direction, wherein the thickness is between about 2.5 nm and about
3.5 nm.
7. The semiconductor device of claim 1, further comprising: a
backside metal line disposed along a bottom surface of the backside
dielectric layer, wherein the through-substrate contact is in
direct contact with the backside metal line.
8. The semiconductor device of claim 1, wherein the
through-substrate contact comprises aluminum (Al), titanium (Ti),
ruthenium (Ru), copper (Cu), nickel (Ni), cobalt (Co), tungsten
(W), or molybdenum (Mo).
9. A semiconductor structure, comprising: a backside dielectric
layer; first channel members over the backside dielectric layer;
second channel members over the backside dielectric layer; a first
gate structure wrapping around each of the first channel members; a
second gate structure wrapping around each of the second channel
members; a dielectric layer disposed over the first gate structure
and the second gate structure; and a through-substrate contact that
extends continuously through the dielectric layer and the backside
dielectric layer.
10. The semiconductor structure of claim 9, wherein the
through-substrate contact comprises a first portion disposed in the
dielectric layer and a second portion disposed in the backside
dielectric layer, wherein a width of the second portion is greater
than a width of the first portion.
11. The semiconductor structure of claim 9, further comprising:
first epitaxial features in contact with end surfaces of the first
channel members; and second epitaxial features in contact with end
surfaces of the second channel members, wherein each of the first
channel members is spaced apart from the through-substrate contact
by one of the first epitaxial features, wherein each of the second
channel members is spaced apart from the through-substrate contact
by one of the second epitaxial features.
12. The semiconductor structure of claim 11, further comprising: a
silicide layer disposed between the first epitaxial features and
the through-substrate contact.
13. The semiconductor structure of claim 11, wherein a portion of
the through-substrate contact extends between two adjacent ones of
the first of epitaxial features.
14. The semiconductor structure of claim 11, wherein the first
channel members are interleaved by a plurality of inner spacer
features, wherein the through-substrate contact is in direct
contact with each of the plurality of inner spacer features.
15. The semiconductor structure of claim 9, further comprising: a
backside metal line disposed along a bottom surface of the backside
dielectric layer, wherein the through-substrate contact is in
direct contact with the backside metal line.
16. A method, comprising: receiving a workpiece comprising: a
fin-shaped structure over a substrate, the fin-shaped structure
comprising a plurality of channel layers, and a first dummy gate
stack and a second dummy gate stack over the fin-shaped structure;
forming a source opening in the fin-shaped structure between the
first dummy gate stack and the second dummy gate stack to expose
sidewalls of the fin-shaped structure; extending the source opening
into the substrate to form an extended source opening; forming a
plurality of epitaxial features over the exposed sidewalls of the
plurality of channel layers; after the forming of the plurality of
epitaxial features, depositing a dummy epitaxial layer into the
extended source opening; replacing the first dummy gate stack and
the second dummy gate stack with a first gate structure and a
second gate structure, respectively, depositing a dielectric layer
over the first gate structure and the second gate structure;
forming a through-substrate opening through the dielectric layer,
the dummy epitaxial layer, and into the substrate, wherein the
plurality of epitaxial features are exposed in the
through-substrate opening; and forming a through-substrate contact
in the through-substrate opening.
17. The method of claim 16, wherein the dummy epitaxial layer
comprises silicon germanium (SiGe).
18. The method of claim 16, wherein the plurality of channel layers
are interleaved by a plurality of sacrificial layers and a
plurality of inner spacer features.
19. The method of claim 18, further comprising: before the forming
of the through-substrate contact, depositing a metal layer in the
through-substrate opening and over the plurality of epitaxial
features; and after the depositing of the metal layer, annealing
the workpiece to form a silicide layer over the plurality of
epitaxial features.
20. The method of claim 16, further comprising replacing the
substrate with a backside dielectric layer.
Description
BACKGROUND
The semiconductor integrated circuit (IC) industry has experienced
exponential growth. Technological advances in IC materials and
design have produced generations of ICs where each generation has
smaller and more complex circuits than the previous generation. In
the course of IC evolution, functional density (i.e., the number of
interconnected devices per chip area) has generally increased while
geometry size (i.e., the smallest component (or line) that can be
created using a fabrication process) has decreased. This scaling
down process generally provides benefits by increasing production
efficiency and lowering associated costs. Such scaling down has
also increased the complexity of processing and manufacturing
ICs.
For example, as integrated circuit (IC) technologies progress
towards smaller technology nodes, multi-gate devices have been
introduced to improve gate control by increasing gate-channel
coupling, reducing off-state current, and reducing short-channel
effects (SCEs). A multi-gate device generally refers to a device
having a gate structure, or portion thereof, disposed over more
than one side of a channel region. Fin-like field effect
transistors (FinFETs) and multi-bridge-channel (MBC) transistors
are examples of multi-gate devices that have become popular and
promising candidates for high performance and low leakage
applications. A FinFET has an elevated channel wrapped by a gate on
more than one side (for example, the gate wraps a top and sidewalls
of a "fin" of semiconductor material extending from a substrate).
An MBC transistor has a gate structure that can extend, partially
or fully, around a channel region to provide access to the channel
region on two or more sides. Because its gate structure surrounds
the channel regions, an MBC transistor may also be referred to as a
surrounding gate transistor (SGT) or a gate-all-around (GAA)
transistor. The channel region of an MBC transistor may be formed
from nanowires, nanosheets, other nanostructures, and/or other
suitable structures. The shapes of the channel region have also
given an MBC transistor alternative names such as a nanosheet
transistor or a nanowire transistor.
As the dimensions of the multi-gate devices shrink, packing all
contact features on one side of a substrate is becoming more and
more challenging. To ease the packing density, it has been proposed
to move some routing features, such as power lines (also referred
to as power rails) to a backside of the substrate. Some processes
for forming backside source/drain contacts may damage the
source/drain features. Additionally, existing structures may not
provide sufficient silicide contact areas. Therefore, while
existing backside power rail formation processes may be generally
adequate for their intended purposes, they are not satisfactory in
all aspects.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is best understood from the following
detailed description when read with the accompanying figures. It is
emphasized that, in accordance with the standard practice in the
industry, various features are not drawn to scale and are used for
illustration purposes only. In fact, the dimensions of the various
features may be arbitrarily increased or reduced for clarity of
discussion.
FIG. 1 illustrates a flow chart of a method for forming a
semiconductor device having a backside power rail, according to one
or more aspects of the present disclosure.
FIGS. 2-16 illustrate fragmentary cross-sectional views of a
workpiece during a fabrication process according to the method of
FIG. 1, according to one or more aspects of the present
disclosure.
DETAILED DESCRIPTION
The following disclosure provides many different embodiments, or
examples, for implementing different features of the provided
subject matter. Specific examples of components and arrangements
are described below to simplify the present disclosure. These are,
of course, merely examples and are not intended to be limiting. For
example, the formation of a first feature over or on a second
feature in the description that follows may include embodiments in
which the first and second features are formed in direct contact,
and may also include embodiments in which additional features may
be formed between the first and second features, such that the
first and second features may not be in direct contact. In
addition, the present disclosure may repeat reference numerals
and/or letters in the various examples. This repetition is for the
purpose of simplicity and clarity and does not in itself dictate a
relationship between the various embodiments and/or configurations
discussed.
Spatially relative terms, such as "beneath," "below," "lower,"
"above," "upper" and the like, may be used herein for ease of
description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. The
spatially relative terms are intended to encompass different
orientations of the device in use or operation in addition to the
orientation depicted in the figures. The apparatus may be otherwise
oriented (rotated 90 degrees or at other orientations) and the
spatially relative descriptors used herein may likewise be
interpreted accordingly.
Further, when a number or a range of numbers is described with
"about," "approximate," and the like, the term is intended to
encompass numbers that are within a reasonable range considering
variations that inherently arise during manufacturing as understood
by one of ordinary skill in the art. For example, the number or
range of numbers encompasses a reasonable range including the
number described, such as within +/-10% of the number described,
based on known manufacturing tolerances associated with
manufacturing a feature having a characteristic associated with the
number. For example, a material layer having a thickness of "about
5 nm" can encompass a dimension range from 4.25 nm to 5.75 nm where
manufacturing tolerances associated with depositing the material
layer are known to be +/-15% by one of ordinary skill in the art.
Still further, the present disclosure may repeat reference numerals
and/or letters in the various examples. This repetition is for the
purpose of simplicity and clarity and does not in itself dictate a
relationship between the various embodiments and/or configurations
discussed.
The present disclosure is generally related to methods of forming a
semiconductor device having backside power rails, and more
particularly to methods of forming a through-substrate source/drain
contact.
Conventionally, source/drain contacts and gate contacts of
transistors on a substrate connect source/drain features of the
transistors to an interconnect structure over a front side of the
substrate. As the dimensions of IC devices shrink, the close
proximity among the source/drain contacts and gate contacts may
reduce process windows for forming these contacts and may increase
parasitic capacitance among them. The backside power rail (BPR)
structure is a modern solution for performance boost on power
delivery network (PDN) for advanced technology node and it eases
the crowding of contacts. In some conventional processes, after a
source/drain feature and a frontside source/drain contact are
formed, the substrate is flipped over and a backside contact
opening is etched from the back side of the substrate. Because the
backside contact opening exposes the source/drain feature, the
formation of the backside contact opening involves risks of
damaging the source/drain feature and adjacent semiconductor
structures. In addition, both the frontside source/drain contact
and the backside source/drain contact interface the source/drain
contact with a silicide layer. The area of the first silicide layer
is largely limited by the contact openings.
The present disclosure provides a source/drain structure for MBC
transistors. In an example structure, a first plurality of channel
members and a second plurality of channel members are disposed over
a backside dielectric layer. A first gate structure is disposed
over and wraps around each of the first plurality of channel
members. A second gate structure is disposed over and wraps around
each of the second plurality of channel members. A
through-substrate source/drain contact extends between the first
plurality of channel members and the second plurality of channel
members. The first plurality of channel members and the second
plurality of channel members are disposed on a backside dielectric
layer. The through-substrate source/drain contact also extends
through the backside dielectric layer. The through-substrate
source/drain contact is spaced apart from the first plurality of
channel members and the second plurality of channel members by a
plurality of epitaxial features. A metal silicide layer and an
adhesion layer may also be disposed between the plurality of
epitaxial features and the through-substrate source/drain contact.
The plurality of epitaxial features are not subject to etching and
their interface with the through-substrate source/drain contact
reduces contact resistance.
The various aspects of the present disclosure will now be described
in more detail with reference to the figures. In that regard, FIG.
1 is a flowchart illustrating method 100 of forming a semiconductor
device according to embodiments of the present disclosure. Method
100 is merely an example and is not intended to limit the present
disclosure to what is explicitly illustrated in method 100.
Additional steps may be provided before, during and after the
method 100, and some steps described can be replaced, eliminated,
or moved around for additional embodiments of the method. Not all
steps are described herein in detail for reasons of simplicity.
Method 100 is described below in conjunction with FIGS. 2-16, which
are fragmentary cross-sectional views of a workpiece 200 at
different stages of fabrication according to embodiments of method
100. Because the workpiece 200 will be fabricated into a
semiconductor device 200 upon conclusion of the fabrication
processes, the workpiece 200 may be referred to as the
semiconductor device 200 as the context requires. Additionally,
throughout the present application, like reference numerals denote
like features, unless otherwise excepted.
Referring to FIGS. 1 and 2, method 100 includes a block 102 where a
workpiece 200 is received. In the depicted embodiment, the
workpiece 200 includes a substrate 202 and a fin-shaped structure
204 disposed over the substrate 202. The fin-shaped structure 204
extends lengthwise along the X direction and is divided into
channel regions 204C, source regions 204S, and drain regions 204D.
In FIG. 2, the workpiece 200 also includes dummy gate stacks 210
disposed over channel regions 204C of the fin-shaped structure 204.
Two dummy gate stacks 210 are shown in FIG. 2 but the workpiece 200
may include more dummy gate stacks 210. The substrate 202 may be a
semiconductor substrate such as a silicon (Si) substrate. The
substrate 202 may also include other semiconductor materials such
as germanium (Ge), silicon carbide (SiC), silicon germanium (SiGe),
or diamond. The fin-shaped structure 204 may be formed from a
portion of the substrate 202 and a vertical stack of alternating
semiconductor layers using a combination of lithography and etch
steps. In some instances, the patterning of the fin-shaped
structure 204 may be performed using double-patterning or
multi-patterning processes to create patterns having pitches
smaller than what is otherwise obtainable using a single, direct
photolithography process. The etching process can include dry
etching, wet etching, reactive ion etching (RIE), and/or other
suitable processes. In the depicted embodiments, the vertical stack
of alternating semiconductor layers may include a plurality of
channel layers 208 and a plurality of sacrificial layers 206. The
plurality of channel layers 208 are interleaved by the plurality of
sacrificial layers 206. In some embodiments, the plurality of
channel layers 208 may include silicon (Si) and the plurality of
sacrificial layers 206 may be formed of silicon germanium (SiGe).
The channel layers 208 and the sacrificial layers 206 may be
epitaxially deposited on the substrate 202 using molecular beam
epitaxy (MBE), vapor-phase epitaxy (VPE), ultra-high vacuum CVD
(UHV-CVD), and/or other suitable epitaxial growth processes.
While not explicitly shown in FIG. 2, an isolation feature is also
formed around the fin-shaped structure 204 to isolate the
fin-shaped structure 204 from an adjacent fin-shaped structure. In
some embodiments, the isolation feature is deposited in trenches
that define the fin-shaped structure 204. Such trenches may extend
through the channel layers 208 and sacrificial layers 206 and
terminate in the substrate 202. The isolation feature may also be
referred to as a shallow trench isolation (STI) feature. In an
example process, a dielectric material for the isolation feature is
deposited over the workpiece 200 using CVD, subatmospheric CVD
(SACVD), flowable CVD, physical vapor deposition (PVD), spin-on
coating, and/or other suitable process. Then the deposited
dielectric material is planarized and recessed until the fin-shaped
structure 204 rises above the isolation feature. The dielectric
material for the isolation feature may include silicon oxide,
silicon oxynitride, fluorine-doped silicate glass (FSG), a low-k
dielectric, combinations thereof, and/or other suitable
materials.
In some embodiments, a gate replacement process (or gate-last
process) is adopted where the dummy gate stacks 210 serve as
placeholders for functional gate structures. Other processes and
configuration are possible. To form the dummy gate stacks 210, a
dummy dielectric layer 211, a dummy gate electrode layer 212, and a
gate-top hard mask layer 215 are deposited over the workpiece 200.
The deposition of these layers may include use of low-pressure CVD
(LPCVD), CVD, plasma-enhanced CVD (PECVD), PVD, thermal oxidation,
e-beam evaporation, or other suitable deposition techniques, or
combinations thereof. The dummy dielectric layer 211 may include
silicon oxide. The dummy gate electrode layer 212 may include
polysilicon. The gate-top hard mask layer 215 may be a multi-layer
that includes a silicon oxide layer 213 and silicon nitride layer
214. Using photolithography and etching processes, the gate-top
hard mask layer 215 is patterned. The photolithography process may
include photoresist coating (e.g., spin-on coating), soft baking,
mask aligning, exposure, post-exposure baking, photoresist
developing, rinsing, drying (e.g., spin-drying and/or hard baking),
other suitable lithography techniques, and/or combinations thereof.
The etching process may include dry etching (e.g., RIE etching),
wet etching, and/or other etching methods. Thereafter, using the
patterned gate-top hard mask 215 as the etch mask, the dummy
dielectric layer 211 and the dummy gate electrode layer 212 are
then etched to form the dummy gate stack 210. As shown in FIG. 2,
portions of the fin-shaped structure 204 underlying the dummy gate
stacks 210 are channel region 204C. The channel regions 204C and
the dummy gate stack 210 also define source regions 204S and drain
regions 204D that are not vertically overlapped by the dummy gate
stacks 210. Each of the channel regions 204C is disposed between a
source region 204S and a drain region 204D along the X
direction.
As shown in FIG. 2, the workpiece 200 also includes a gate spacer
layer 216 disposed along sidewalls of the dummy gate stacks 210 and
top surfaces of the fin-shaped structure 204. In some embodiments,
the formation of the gate spacer layer 216 includes conformal
deposition of one or more dielectric layers over the workpiece 200.
In an example process, the one or more dielectric layers are
deposited using CVD, SACVD, or ALD. The one or more dielectric
layers may include silicon oxide, silicon nitride, silicon carbide,
silicon oxynitride, silicon carbonitride, silicon oxycarbide,
silicon oxycarbonitride, and/or combinations thereof.
Referring to FIGS. 1 and 3, method 100 includes a block 104 where a
source region 204S and a drain region 204D of the fin-shaped
structure 204 are recessed to form a source opening 222S and a
drain opening 222D. After the deposition of the gate spacer layer
216, the dummy gate stacks 210 and the gate spacer layer 216 along
sidewalls of the dummy gate stacks serve as an etch mask in an etch
process that anisotropically etches the source regions 204S and the
drain regions 204D of the fin-shaped structure 204. The anisotropic
etching of the source regions 204S and the drain regions 204D
results in source openings 222S and drain openings 222D,
respectively. The etch process at block 104 may be a dry etch
process or a suitable etch process. An example dry etch process may
implement an oxygen-containing gas, hydrogen, a fluorine-containing
gas (e.g., CF.sub.4, SF.sub.6, CH.sub.2F.sub.2, CHF.sub.3, and/or
C.sub.2F.sub.6), a chlorine-containing gas (e.g., Cl.sub.2,
CHCl.sub.3, CCl.sub.4, and/or BCl.sub.3), a bromine-containing gas
(e.g., HBr and/or CHBr.sub.3), an iodine-containing gas, other
suitable gases and/or plasmas, and/or combinations thereof. In
embodiments represented in FIG. 3, the source openings 222S and the
drain openings 222D extend through vertical stack of semiconductor
layers (including channel layers 208 and sacrificial layers 206).
In some implementations not explicitly shown, the source openings
222S and the drain openings 222D may partially extend into the
substrate 202. Sidewalls of the channel layers 208 and the
sacrificial layers 206 are exposed in the source openings 222S and
the drain openings 222D.
Referring to FIGS. 1 and 3, method 100 includes a block 106 where
inner spacer features 218 are formed. After the formation of the
source openings 222S and the drain openings 222D, the sacrificial
layers 206 exposed in the source openings 222S and the drain
openings 222D are selectively and partially recessed to form inner
spacer recesses (not explicitly shown), while the exposed channel
layers 208 are substantially unetched. In an embodiment where the
channel layers 208 consist essentially of silicon (Si) and
sacrificial layers 206 consist essentially of silicon germanium
(SiGe), the selective and partial recess of the sacrificial layers
206 may include use of a selective isotropic etching process (e.g.,
a selective dry etching process or a selective wet etching
process), and the extent at which the sacrificial layers 206 are
recessed is controlled by duration of the etching process. The
selective dry etching process may include use of one or more
fluorine-based etchants, such as fluorine gas or
hydrofluorocarbons. The selective wet etching process may include
an APM etch (e.g., ammonia hydroxide-hydrogen peroxide-water
mixture). After the formation of the inner spacer recesses, an
inner spacer material layer is deposited over the workpiece 200,
including in the inner spacer recesses. The inner spacer material
layer may include silicon oxide, silicon nitride, silicon
oxycarbide, silicon oxycarbonitride, silicon carbonitride, metal
nitride, or a suitable dielectric material. The deposited inner
spacer material layer is then etched back to remove excess inner
spacer material layer over sidewalls of the channel layers 208,
thereby forming the inner spacer features 218 as shown in FIG. 3.
In some embodiments, the etch back process at block 106 may be a
dry etch process that includes use of an oxygen-containing gas,
hydrogen, nitrogen, a fluorine-containing gas (e.g., CF.sub.4,
SF.sub.6, CH.sub.2F.sub.2, CHF.sub.3, and/or C.sub.2F.sub.6), a
chlorine-containing gas (e.g., Cl.sub.2, CHCl.sub.3, CCl.sub.4,
and/or BCl.sub.3), a bromine-containing gas (e.g., HBr and/or
CHBr.sub.3), an iodine-containing gas (e.g., CF.sub.3I), other
suitable gases and/or plasmas, and/or combinations thereof.
Referring to FIGS. 1 and 4, method 100 includes a block 108 where
the source opening 222S is selectively extended into the substrate
202 to form an extended source opening 2220. At block 108, a first
mask film 220 is formed over the workpiece 200, as shown in FIG. 4.
The first mask film 220 may be a hard mask layer. The first mask
film 220 may include silicon oxide, silicon nitride, silicon
oxynitride, silicon oxycarbonitride, silicon carbide, or silicon
oxycarbide. In an example process, a dielectric material is
deposited over the workpiece using CVD or ALD to form the first
mask film 220 and then a photoresist layer is deposited over the
first mask film 220 using spin-on coating or a suitable process.
The photoresist layer is patterned using photolithography processes
to form a patterned photoresist layer. The patterned photoresist
layer is then applied as an etch mask in an etch process to pattern
the first mask film 220. As shown in FIG. 4, the patterned first
mask film 220 cover/protect the drain openings 222D while the
source opening 222S is exposed. An anisotropic etch process is then
performed to extend the source opening 222S further into the
substrate 202 to form an extended source opening 2220. In some
instances, the extended source opening 2220 may extend between
about 15 nanometer (nm) and about 35 nm into the substrate 202. In
some implementations, the anisotropic etch process at block 108 may
be a dry etch process that uses an oxygen-containing gas, hydrogen,
a fluorine-containing gas (e.g., CF.sub.4, SF.sub.6,
CH.sub.2F.sub.2, CHF.sub.3, and/or C.sub.2F.sub.6), a
chlorine-containing gas (e.g., Cl.sub.2, CHCl.sub.3, CCl.sub.4,
and/or BCl.sub.3), a bromine-containing gas (e.g., HBr and/or
CHBR.sub.3), an iodine-containing gas, other suitable gases and/or
plasmas, and/or combinations thereof.
Referring to FIGS. 1 and 5, method 100 includes a block 110 where a
plurality of epitaxial source features 226 are formed in the
extended source opening 2220 to be in contact with sidewalls of the
channel layers 208. In some embodiments, the epitaxial source
features 226 may be deposited using an epitaxial deposition
process, such as VPE, UHV-CVD, MBE, and/or other suitable
processes. The epitaxial growth process may use gaseous and/or
liquid precursors, which selectively interact with the
semiconductor composition of the channel layers 208 and the
substrate 202. That is, the plurality of epitaxial source features
226 are deposited on exposed surfaces of the channel layers 208 and
the substrate 202 in the extended source opening 2220. Each of the
plurality of epitaxial source features 226 is therefore coupled to
one of the channel layers 208. According to the present disclosure,
while the plurality of epitaxial source features 226 may moderately
grow over a portion of the inner spacer features 218, they do not
merge to form a continuous epitaxial layer. At block 110, a bottom
epitaxial feature 226B may also be formed on the exposed surfaces
of the substrate 202. In some embodiments, the bottom epitaxial
feature 226B is spaced apart from the bottommost epitaxial source
features 226. Depending on the conductivity type of the
to-be-formed transistor, the epitaxial source features 226 may be
n-type or p-type. Example n-type epitaxial source features may
include silicon (Si), phosphorus-doped silicon (Si:P),
arsenic-doped silicon (Si:As), antimony-doped silicon (Si:Sb), or
other suitable material and may be in-situ doped during the
epitaxial process by introducing an n-type dopant, such as
phosphorus (P), arsenic (As), or antimony (Sb). Example p-type
epitaxial source features 226 may include germanium (Ge),
gallium-doped silicon germanium (SiGe: Ga), boron-doped silicon
germanium (SiGe:B), or other suitable material and may be in-situ
doped during the epitaxial process by introducing a p-type dopant,
such as boron (B) or gallium (Ga). As shown in FIG. 5, when viewed
along the Y direction, each of the epitaxial source features 226
may have an elongated island shape or a ridge that extends
lengthwise along the Y direction. In some instances, when measured
along the X direction, each of the epitaxial source features 226
may have a thickness between about 2.5 nm and about 4.5 nm.
Referring to FIGS. 1 and 6, method 100 includes a block 112 where a
sacrificial epitaxial layer 228 is deposited. In some embodiments,
the sacrificial epitaxial layer 228 may include a semiconductor
material different from the epitaxial source features 226 or the
bottom epitaxial feature 226B. For example, when the epitaxial
source features 226 or the bottom epitaxial feature 226B includes
silicon (Si), the sacrificial epitaxial layer 228 may include
silicon germanium (SiGe). When the epitaxial source features 226 or
the bottom epitaxial feature 226B includes silicon germanium
(SiGe), the sacrificial epitaxial layer 228 may include silicon
(Si), germanium (Ge), or germanium-rich silicon germanium (SiGe).
Difference in the semiconductor material allows the sacrificial
epitaxial layer 228 to be removed without substantially damaging
the epitaxial source features 226. The sacrificial epitaxial layer
228 may be doped or undoped. When the sacrificial epitaxial layer
228 is doped, it is doped with the same type of dopant in the
epitaxial source features 226 and its doping concentration is
smaller than that of the epitaxial source feature 226. As the
sacrificial epitaxial layer 228 will be removed in a subsequent
process, its composition or doping concentration is determined
based the desired etching selectivity with respect to the epitaxial
source features 226. The sacrificial epitaxial layer 228 may also
be referred to as a dummy epitaxial layer. In some embodiments, the
dummy epitaxial layer 228 may be formed using VPE, UHV-CVD, MBE,
and/or other suitable processes. After the formation of the
sacrificial epitaxial layer 228, the first mask film 220 may be
removed from the workpiece 200.
Referring to FIGS. 1, 7 and 8, method 100 includes a block 114
where a drain feature 232 is formed. At block 114, a second mask
film 230 is formed over the workpiece 200, as shown in FIG. 7. The
second mask film 230 may be a patterned hard mask layer. The second
mask film 230 may include silicon oxide, silicon nitride, silicon
oxynitride, silicon oxycarbonitride, silicon carbide, or silicon
oxycarbide. In an example process, a dielectric material is
deposited over the workpiece using CVD or ALD to form the second
mask film 230 and then a photoresist layer is deposited over the
second mask film 230 using spin-on coating or a suitable process.
The photoresist layer is patterned using photolithography processes
to form a patterned photoresist layer. The patterned photoresist
layer is then applied as an etch mask in an etch process to pattern
the second mask film 230. As shown in FIG. 7, the patterned second
mask film 230 cover/protect the source openings 222S while the
drain opening 222D is exposed.
Reference is now made to FIG. 8. In some embodiments, the drain
feature 232 may be deposited using an epitaxial process, such as
VPE, UHV-CVD, MBE, and/or other suitable processes. The epitaxial
growth process may use gaseous and/or liquid precursors, which
interact with the composition of the channel layers 208 and the
substrate 202. The drain feature 232 is therefore coupled to the
channel layers 208. Depending on the conductivity type of the
to-be-formed transistor, the drain feature 232 may be an n-type
drain feature or a p-type drain features. Example n-type
source/drain features may include silicon (Si), phosphorus-doped
silicon (Si:P), arsenic-doped silicon (Si:As), antimony-doped
silicon (Si:Sb), or other suitable material and may be in-situ
doped during the epitaxial process by introducing an n-type dopant,
such as phosphorus (P), arsenic (As), or antimony (Sb). Example
p-type source/drain features may include germanium (Ge),
gallium-doped silicon germanium (SiGe: Ga), boron-doped silicon
germanium (SiGe:B), or other suitable material and may be in-situ
doped during the epitaxial process by introducing a p-type dopant,
such as boron (B) or gallium (Ga). Although the deposition of the
drain feature 232 may be substantially selective to semiconductor
surfaces, overgrowth of the drain feature 232 may merge over the
inner spacer features 218. That is, the drain feature 232 may come
in direct contact with both the inner spacer features 218 and the
channel layers 208.
Referring to FIGS. 1 and 9, method 100 includes a block 116 where a
contact etch stop layer (CESL) 240 and a first interlayer
dielectric layer 242 are deposited. The CESL 240 may include
silicon nitride, silicon oxynitride, and/or other materials known
in the art and may be formed by ALD, plasma-enhanced chemical vapor
deposition (PECVD) process and/or other suitable deposition or
oxidation processes. As shown in FIG. 9, the CESL 240 may be
deposited on top surfaces of the sacrificial epitaxial layer 228,
the drain features 232, and sidewalls of the gate spacer layer 216.
The first ILD layer 242 is then deposited by a PECVD process or
other suitable deposition technique over the workpiece 200 after
the deposition of the CESL 240. The first ILD layer 242 may include
materials such as tetraethylorthosilicate (TEOS) oxide, un-doped
silicate glass, or doped silicon oxide such as borophosphosilicate
glass (BPSG), fused silica glass (FSG), phosphosilicate glass
(PSG), boron doped silicon glass (BSG), and/or other suitable
dielectric materials. In some embodiments, after formation of the
first ILD layer 242, the workpiece 200 may be annealed to improve
integrity of the first ILD layer 242.
Referring to FIGS. 1 and 10, method 100 includes a block 118 where
the dummy gate stacks 210 are replaced with gate structures 250. To
remove excess materials and to expose top surfaces of the dummy
gate stacks 210, a planarization process, such a chemical
mechanical polishing (CMP) process may be performed to the
workpiece 200. With the exposure of the dummy gate stacks 210,
block 118 proceeds to removal of the dummy gate stacks 210. The
removal of the dummy gate stacks 210 may include one or more
etching processes that are selective to the material in the dummy
gate stacks 210. For example, the removal of the dummy gate stacks
210 may be performed using as a selective wet etch, a selective dry
etch, or a combination thereof. After the removal of the dummy gate
stacks 210, sidewalls and top surfaces of the channel layers 208
and the sacrificial layers 206 are exposed. After the removal of
the dummy gate stacks 210, the sacrificial layers 206 in the
channel regions 204C are selectively removed to release the channel
layers 208 as channel members 2080. In some example processes, the
sacrificial layers 206 may be removed using selective dry etch
process or selective wet etch process. The selective dry etch
process may include use of one or more fluorine-based etchants,
such as fluorine gas or hydrofluorocarbons. The selective wet
etching process may include an APM etch (e.g., ammonia
hydroxide-hydrogen peroxide-water mixture).
Block 118 also includes operations to deposit gate structures 250
in the channel regions 204C. As shown in FIG. 10, each of the gate
structures 250 is deposited to wrap around each of the channel
members 2080. Each of the gate structures 250 may include an
interfacial layer, a gate dielectric layer over the interfacial
layer and a gate electrode layer over the gate dielectric layer. In
some embodiments, the interfacial layer includes silicon oxide and
may be formed in a pre-clean process. An example pre-clean process
may include use of RCA SC-1 (a mixture of ammonium hydroxide,
hydrogen peroxide and water) and/or RCA SC-2 (a mixture of
hydrochloric acid, hydrogen peroxide and water). The gate
dielectric layer may also be referred to a high-k dielectric layer,
as it is formed of a dielectric material having a dielectric
constant greater than that of silicon dioxide, which is about 3.9.
The gate dielectric layer may be deposited over the interfacial
layer using ALD, CVD, and/or other suitable methods. The gate
dielectric layer may include hafnium oxide. Alternatively, the gate
dielectric layer may include other high-K dielectrics, such as
titanium oxide (TiO.sub.2), hafnium zirconium oxide (HfZrO),
tantalum oxide (Ta.sub.2O.sub.5), hafnium silicon oxide
(HfSiO.sub.4), zirconium oxide (ZrO.sub.2), zirconium silicon oxide
(ZrSiO.sub.2), lanthanum oxide (La.sub.2O.sub.3), aluminum oxide
(Al.sub.2O.sub.3), zirconium oxide (ZrO), yttrium oxide
(Y.sub.2O.sub.3), SrTiO.sub.3 (STO), BaTiO.sub.3 (BTO), BaZrO,
hafnium lanthanum oxide (HfLaO), lanthanum silicon oxide (LaSiO),
aluminum silicon oxide (AlSiO), hafnium tantalum oxide (HfTaO),
hafnium titanium oxide (HfTiO), (Ba,Sr)TiO.sub.3 (BST), silicon
nitride (SiN), silicon oxynitride (SiON), combinations thereof, or
other suitable material.
The gate electrode layer is then deposited over the gate dielectric
layer using ALD, PVD, CVD, e-beam evaporation, or other suitable
methods. The gate electrode layer may include a single layer or
alternatively a multi-layer structure, such as various combinations
of a metal layer with a selected work function to enhance the
device performance (work function metal layer), a liner layer, a
wetting layer, an first adhesion layer, a metal alloy or a metal
silicide. By way of example, the gate electrode layer may include
titanium nitride (TiN), titanium aluminum (TiAl), titanium aluminum
nitride (TiAlN), tantalum nitride (TaN), tantalum aluminum (TaAl),
tantalum aluminum nitride (TaAlN), tantalum aluminum carbide
(TaAlC), tantalum carbonitride (TaCN), aluminum (Al), tungsten (W),
nickel (Ni), titanium (Ti), ruthenium (Ru), cobalt (Co), platinum
(Pt), tantalum carbide (TaC), tantalum silicon nitride (TaSiN),
copper (Cu), other refractory metals, or other suitable metal
materials or a combination thereof. Further, where the
semiconductor device 200 includes n-type transistors and p-type
transistors, different gate electrode layers may be formed
separately for n-type transistors and p-type transistors, which may
include different work function metal layers (e.g., for providing
different n-type and p-type work function metal layers). In some
instances, the workpiece 200 may be subject to a CMP process to
provide a planar top surface.
Referring to FIGS. 1 and 11, method 100 includes a block 120 where
a second ILD layer 248 is deposited over the workpiece 200. After
the gate structures 250 are formed and the workpiece 200 is
planarized, a second ILD layer 248 may be deposited over the
workpiece 200. As the composition and the formation of the second
ILD layer 248 may be similar to the first ILD layer 242, detailed
description of the second ILD layer 248 are omitted for brevity. In
some embodiments represented in FIG. 11, before the deposition of
the second ILD layer 248, a capping layer 246 may be deposited over
the workpiece 200 to protect the gate structures 250. In some
instances, the capping layer 246 may include silicon nitride or
silicon carbonitride. The capping layer 246 may be deposited using
CVD, ALD, or a suitable deposition process.
Referring to FIGS. 1 and 11, method 100 includes a block 122 where
a through-substrate source contact 260 is formed. Operations at
block 122 may include formation of a through-substrate source
contact opening, formation of a first silicide layer 262, formation
of a first adhesion layer 264, and deposition of a metal fill
material in the through-substrate source contact opening to form
the through-substrate source contact 260. Formation of the
through-substrate source contact opening may include
photolithography processes and etch processes. In an example, a
patterned hard mask may be formed over the workpiece 200. The
patterned hard mask is then applied as an etch mask to etch through
the second ILD layer 248, the capping layer 246, the first ILD
layer 242, the CESL 240, and the sacrificial epitaxial layer 228.
In some embodiments, the etch process may include more than one
stage. For example, the etch process may include a first stage and
second stage. The first stage may include anisotropic dry etch
directed to etching of the second ILD layer 248, the capping layer
246, the first ILD layer 242, the CESL 240. The second stage may
include selective etching of the sacrificial epitaxial layer 228
without substantially damaging the epitaxial source features 226.
For example, the second stage may implement a selective wet etch
process or a selective dry etch process. In the depicted
implementations, the etch process at block 122 substantially
removes the sacrificial epitaxial layer 228 to expose the epitaxial
source features 226 and the bottom epitaxial feature 226B. In some
instances, the etch process at block 122 may be anisotropic and may
reduce a thickness of the bottom epitaxial feature 226B.
In order to reduce contact resistance between the epitaxial source
features 226 and the through-substrate source contact 260, the
first silicide layer 262 may be formed on the exposed surface of
the epitaxial source features 226 in the through-substrate source
contact opening. To form the first silicide layer 262, a metal
layer is deposited over the exposed surfaces of the epitaxial
source features 226 and an anneal process is performed to bring
about silicidation reaction between the metal layer and the
epitaxial source features 226. Suitable metal layer may include
titanium (Ti), tantalum (Ta), nickel (Ni), cobalt (Co), or tungsten
(W). The first silicide layer 262 may include titanium silicide
(TiSi), titanium silicon nitride (TiSiN), tantalum silicide (TaSi),
tungsten silicide (WSi), cobalt silicide (CoSi), or nickel silicide
(NiSi). The first silicide layer 262 generally tracks the shape of
the epitaxial source features 226. Although not explicitly shown,
the excess metal layer that does not form the first silicide layer
262 may be removed. In some embodiments, the metal layer may also
be deposited on the bottom epitaxial feature 226B and the annealing
may also form the first silicide layer 262 on the bottom epitaxial
feature 226B. After the formation of the first silicide layer 262,
the first adhesion layer 264 may be formed by depositing a metal
layer using CVD, follow by nitridation of the metal layer. In some
implementations, the deposition of the metal layer is configured
such that the metal layer is selectively deposited on the first
silicide layer 262 but not on the dielectric surfaces, such as the
surfaces of the inner spacer features 218, the first ILD layer 242,
or the second ILD layer 248. The nitridation process may include
use of a nitrogen-containing gas such as nitrogen or ammonia and
may be aided by plasma. The nitridation process converts the metal
layer into a metal nitride layer. In some instances, the metal
layer may include titanium (Ti), tantalum (Ta), nickel (Ni), cobalt
(Co), or tungsten (W) and the first adhesion layer 264 may include
titanium nitride (TiN), cobalt nitride (CoN), nickel nitride (NiN),
tungsten nitride (WN), or tantalum nitride (TaN). In one
embodiment, the metal layer includes titanium (Ti) and the first
adhesion layer 264 includes titanium nitride (TiN). In some
instances, both the first silicide layer 262 and the first adhesion
layer 264 may have a thickness between about 1 nm and about 3
nm.
After the formation of the first silicide layer 262 and the first
adhesion layer 264, a metal fill layer 261 may be deposited into
the through-substrate source contact opening to form the
through-substrate source contact 260. The metal fill layer 261 may
include aluminum (Al), rhodium (Rh), molybdenum (Mo), cobalt (Co),
ruthenium (Ru), copper (Cu), iridium (Ir), or tungsten (W). A
planarization process, such as a CMP process, may follow to remove
excess materials over the second ILD layer 248 and provide a planar
top surface. The through-substrate source contact 260 is
electrically coupled to the epitaxial source features 226 by way of
the first silicide layer 262 and the first adhesion layer 264. In
other words, the first silicide layer 262 and the first adhesion
layer 264 are sandwiched between the epitaxial source features 226
and the through-substrate source contact 260. As shown in FIG. 11,
a portion of the through-substrate source contact 260 may extend
into two adjacent ones of the epitaxial source features 226.
Additionally, if the first adhesion layer 264 may be viewed as a
part of or an extension of the through-substrate source contact
260, the through-substrate source contact 260 is in direct contact
with the inner spacer features 218.
Although not explicitly shown, before the workpiece 200 is flipped
over for operations from the back side of the workpiece 200, an
interconnect structure may be formed over the workpiece 200. In
some embodiments, the interconnect structure may include multiple
intermetal dielectric (IMD) layers and multiple metal lines or
contact vias in each of the IMD layers. In some instances, the IMD
layers and the first ILD layer 242 may share similar composition.
The metal lines and contact vias in each IMD layer may be formed of
metal, such as aluminum (Al), tungsten (W), ruthenium (Ru), or
copper (Cu). In some embodiments, the metal lines and contact vias
may be lined by a barrier layer to insulate the metal lines and
contact vias from the IMD layers and to prevent
electro-migration.
Referring to FIGS. 1, 12, 13, and 14, method 100 includes a block
124 where a backside dielectric layer 270 is formed. In some
embodiments, operations at block 124 may be performed with a back
side of the workpiece 200 facing up. In an example process to flip
the workpiece 200 over, a carrier substrate is bonded to the front
side of the workpiece 200 or the interconnect structure. The
workpiece 200 is then flipped over along with the carrier
substrate. In some instances, the carrier substrate may be bonded
to the workpiece 200 by fusion bonding, by use of an adhesion
layer, or a combination thereof. In some instances, the carrier
substrate may be formed of semiconductor materials (such as
silicon), sapphire, glass, polymeric materials, or other suitable
materials. In embodiments where fusion bonding is used, the carrier
substrate includes a bottom oxide layer and the workpiece 200 (or
the interconnect structure, if formed)) includes a top oxide layer.
After both the bottom oxide layer and top oxide layer are treated,
they are placed in plush contact with one another for direct
bonding at room temperature or at an elevated temperature. After
the carrier substrate is bonded to the workpiece 200 (or the
interconnect structure, if formed), the workpiece 200 is flipped
up-side-down, as representatively shown in FIG. 12.
After the workpiece 200 is flipped over, a back side of the
workpiece 200 is planarized until the isolation feature and the
through-substrate source contact 260 are exposed. The planarization
may remove a portion of the substrate 202 and a portion of the
bottom epitaxial feature 226B. Referring to FIG. 13 and FIG. 14,
the remaining substrate 202 is then replaced with a backside
dielectric layer 270. The replacement process includes a selective
removal of the substrate 202 without substantially damaging the
bottom epitaxial feature 226B and the through-substrate source
contact 260, as shown in FIG. 13. This selective removal is made
possible by the fact that the substrate 202 have different
compositions from surrounding structures, such the isolation
feature (i.e., STI), the first silicide layer 262, the first
adhesion layer 264, the bottom epitaxial feature 226B, and the
metal fill layer 261. After the substrate 202 is selectively
removed, the backside dielectric layer 270 may be deposited over a
back side of the workpiece 200 by FCVD, CVD, PECVD, spin-on
coating, or a suitable process. After the formation of the backside
dielectric layer 270, the back side of the workpiece 200 is
planarized by a CMP process to expose a surface of the
through-substrate source contact 260, as shown in FIG. 14. In some
embodiments, before the deposition of the backside dielectric layer
270, a protective layer 268 may be deposited over the backside of
the workpiece 200. In some embodiments, the backside dielectric
layer 270 may include silicon oxide or a composition similar to
that of the first ILD layer 242. The protective layer 268 may
include silicon nitride or silicon carbonitride and may be
deposited using CVD, ALD, or a suitable deposition technique.
Referring to FIGS. 1 and 15, method 100 includes a block 126 where
a backside power rail 290 is formed. While not explicitly shown in
FIG. 15, the backside power rail 290 may be embedded in an
insulation layer. In an example process, an insulation layer having
a composition similar to the first ILD layer 242 may be deposited
over the backside of the workpiece 200, including over the backside
dielectric layer 270, the isolation feature, and the backside
surface of the through-substrate source contact 260. Then, a power
rail trench may be patterned in the insulation layer. A barrier
layer and a metal fill material are then deposited into the power
rail trench to form the backside power rail 290. In some
embodiments, the barrier layer in the backside power rail 290 may
include titanium nitride, tantalum nitride, cobalt nitride, nickel
nitride, or tungsten nitride and the metal fill material in the
backside power rail 290 may include titanium (Ti), ruthenium (Ru),
copper (Cu), nickel (Ni), cobalt (Co), tungsten (W), tantalum (Ta),
or molybdenum (Mo). The barrier layer and the metal fill layer may
be deposited using PVD, CVD, ALD, or electroless plating. A
planarization process, such as a CMP process, may be performed to
remove excess materials over the insulation layer. The backside
power rail 290 is electrically coupled to the through-substrate
source contact 260.
FIG. 16 illustrates an additional example where a frontside drain
contact 306 is formed. The frontside drain contact opening may be
formed simultaneously with the through-substrate source contact
opening in some embodiments. As shown in FIG. 16, the frontside
drain contact opening is formed through the second ILD layer 248,
the capping layer 246, the first ILD layer 242, and the CESL 240 to
expose the drain feature 232. To lower contact resistance, a second
silicide layer 302 is formed on the drain feature 232. To improve
adhesion, a second adhesion layer 304 may be formed over the second
silicide layer 302. The composition and formation of the second
silicide layer 302 may be similar to the first silicide layer 262.
The composition and formation of the second adhesion layer 304 may
be similar to those of the first adhesion layer 264. As both the
first silicide layer 262 and the first adhesion layer 264 are
described above, detailed description of the second silicide layer
302 and the second adhesion layer 304 are omitted. In the example
illustrated in FIG. 16, a metal line 308 may be formed over the
frontside drain contact 306. The composition and formation of the
metal line 308 may be similar to those of the backside power rail
290. The metal line 308 may be part of the interconnect structure
described above. Because the metal line 308 is the first metal line
over the gate structures 250, the metal line 308 may also be
referred to as M.sub.0 line in an M.sub.0 layer of the interconnect
structure.
In some embodiments represented in FIG. 16, the through-substrate
source contact 260 may include a backside portion disposed in the
backside dielectric layer 270, a source portion disposed between
epitaxial source features 226, and a frontside portion disposed in
the second ILD layer 248. The backside portion includes a first
width W1 along the X direction, the source portion includes a
second width W2 along the X direction, and the frontside portion
includes a third width W3 along the X direction. In some
embodiments, the first width W1 is greater than the third width W3
and the third width W3 is greater than the second width W2. In some
instances, the first width W1 may be between about 15 nm and about
22 nm, the second width W2 may be between about 12 nm and about 16
nm, and the third width W3 may be between about 12 nm and about 18
nm. Each of the gate structures 250 may have a gate length L
between 13 nm and about 19 nm and the gate structures 250 may
include a gate pitch P between about 40 nm and about 50 nm.
Embodiments of the present disclosure provide advantages. For
example, a semiconductor device of the present disclosure includes
a through-substrate source contact that extends from a front side
of the semiconductor device to a back side of the semiconductor
device. As a result, separate backside source contact openings are
not needed and the risks of damages to source features are avoided.
In addition, the through-substrate source contact engages the
plurality of epitaxial source features that resemble elongated
islands or ridges. Such an engagement increases the interfacial
areas between the through-substrate source contact and the
epitaxial source features, thereby reducing contact resistance.
In one exemplary aspect, the present disclosure is directed to a
semiconductor device. The semiconductor device includes a first
plurality of channel members over a backside dielectric layer, a
second plurality of channel members over the backside dielectric
layer, a first gate structure over and wrapping around each of the
first plurality of channel members, a second gate structure over
and wrapping around each of the second plurality of channel
members, and a through-substrate contact that extends between the
first plurality of channel members and the second plurality of
channel members, between the first gate structure and the second
gate structure, and through the backside dielectric layer.
In some embodiments, the semiconductor device may further include a
first plurality of epitaxial features in contact with the first
plurality of channel members, and a second plurality of epitaxial
features in contact with the second plurality of channel members.
Each of the first plurality of channel members is spaced apart from
the through-substrate contact by one of the first plurality of
epitaxial features and each of the second plurality of channel
members is spaced apart from the through-substrate contact by one
of the second plurality of epitaxial features. In some
implementations, the semiconductor device may further include a
silicide layer disposed between the first plurality of epitaxial
features and the through-substrate contact. In some instances, a
portion of the through-substrate contact extends between two
adjacent epitaxial features of the first plurality of epitaxial
features. In some embodiments, the first plurality of channel
members are interleaved by a plurality of inner spacer features and
the through-substrate contact is in direct contact with each of the
plurality of inner spacer features. In some embodiments, the first
plurality of channel members and the second plurality of channel
members extend lengthwise along a direction. Each of the first
plurality of epitaxial feature includes a thickness along the
direction and the thickness is between about 2.5 nm and about 3.5
nm. In some embodiments, the semiconductor device may further
include a backside metal line disposed along a bottom surface of
the backside dielectric layer. The through-substrate contact is in
direct contact with the backside metal line. In some instances, the
through-substrate contact includes aluminum (Al), titanium (Ti),
ruthenium (Ru), copper (Cu), nickel (Ni), cobalt (Co), tungsten
(W), or molybdenum (Mo).
In another exemplary aspect, the present disclosure is directed to
a semiconductor structure. The semiconductor structure includes a
backside dielectric layer, first channel members over the backside
dielectric layer, second channel members over the backside
dielectric layer, a first gate structure wrapping around each of
the first channel members, a second gate structure wrapping around
each of the second channel members, a dielectric layer disposed
over the first gate structure and the second gate structure, and a
through-substrate contact that extends continuously through the
dielectric layer and the backside dielectric layer.
In some embodiments, the through-substrate contact includes a first
portion disposed in the dielectric layer and a second portion
disposed in the backside dielectric layer and a width of the second
portion is greater than a width of the first portion. In some
implementations, the semiconductor device may further include first
epitaxial features in contact with end surfaces of the first
channel members, and second epitaxial features in contact with end
surfaces of the second channel members. Each of the first channel
members is spaced apart from the through-substrate contact by one
of the first epitaxial features. Each of the second channel members
is spaced apart from the through-substrate contact by one of the
second epitaxial features. In some implementations, the
semiconductor structure may further include a silicide layer
disposed between the first epitaxial features and the
through-substrate contact. In some instances, a portion of the
through-substrate contact extends between two adjacent ones of the
first of epitaxial features. In some embodiments, the first channel
members are interleaved by a plurality of inner spacer features and
the through-substrate contact is in direct contact with each of the
plurality of inner spacer features. In some instances, the
semiconductor structure may further include a backside metal line
disposed along a bottom surface of the backside dielectric layer.
The through-substrate contact is in direct contact with the
backside metal line.
In yet another exemplary aspect, the present disclosure is directed
to a method. The method includes receiving a workpiece that
includes a fin-shaped structure over a substrate, the fin-shaped
structure including a plurality of channel layers, and a first
dummy gate stack and a second dummy gate stack over the fin-shaped
structure, forming a source opening in the fin-shaped structure
between the first dummy gate stack and the second dummy gate stack
to expose sidewalls of the fin-shaped structure, extending the
source opening into the substrate to form an extended source
opening, forming a plurality of epitaxial features over the exposed
sidewalls of the plurality of channel layers, after the forming of
the plurality of epitaxial features, depositing a dummy epitaxial
layer into the extended source opening, replacing the first dummy
gate stack and the second dummy gate stack with a first gate
structure and a second gate structure, respectively, depositing a
dielectric layer over the first gate structure and the second gate
structure, forming a through-substrate opening through the
dielectric layer, the dummy epitaxial layer, and into the
substrate, wherein the plurality of epitaxial features are exposed
in the through-substrate opening, and forming a through-substrate
contact in the through-substrate opening.
In some embodiments, the dummy epitaxial layer includes silicon
germanium (SiGe). In some embodiments, the plurality of channel
layers are interleaved by a plurality of sacrificial layers and a
plurality of inner spacer features. In some implementations, the
method may further include before the forming of the
through-substrate contact, depositing a metal layer in the
through-substrate opening and over the plurality of epitaxial
features, and after the depositing of the metal layer, annealing
the workpiece to form a silicide layer over the plurality of
epitaxial features. In some instances, the method may further
include replacing the substrate with a backside dielectric
layer.
The foregoing outlines features of several embodiments so that
those of ordinary skill in the art may better understand the
aspects of the present disclosure. Those of ordinary skill in the
art should appreciate that they may readily use the present
disclosure as a basis for designing or modifying other processes
and structures for carrying out the same purposes and/or achieving
the same advantages of the embodiments introduced herein. Those of
ordinary skill in the art should also realize that such equivalent
constructions do not depart from the spirit and scope of the
present disclosure, and that they may make various changes,
substitutions, and alterations herein without departing from the
spirit and scope of the present disclosure.
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